Idle too high after sync

Hello,

I recently shimmed my valves back in spec-three were nearing zero clearance as the PO never checked them for 22,000 miles.
I did a carb sync today and now the bike idles at 1500 rpm.
The idle adjusting screw is backed off all the way and I can't get lower than 1500.
Before syncing the idle was at 1050.
Can anyone point me in the right direction?

Thanks, Maz

 

You probably adjusted yourself out of adjustment.

When you did the bench sync, if you started with the linkage adjusted too far "down" so when sync'ing, you ran yourself out of adjustment.

Unfortunately, the "fix" is to start over, with the main knob screwed in further to begin with.

Did you sync with the YICS blocked?

 

That is what I suspected.
I skipped one fundamental step- I did not bench sync the carbs.
My Achilles heel is pulling apart carbs. I "rebuilt" the carb on my boat motor and it never ran again....
Bigfitz-I did make and use a YICS tool per instructions on the forum and it works very good.
So did my 10 buck sync tool.
I will do a Bench Sync forum search, face my worst fears and pull the rack.
Until I do the carbs,would riding the bike with the high idle hurt anything.?

Maz

 

hold on Maz, try this, turn the idle knob till the idle goes up to 1600 or even 1800 (keep a fan blowing right on the engine) then sync 3 and 4 with the screw on the brake side, then do 1 and 2 with the screw on the shifter side, then 12/34 with the center screw.
somewhere along the line the idle should shoot up, just turn it down as needed, start with the mixture screws about 2.75 turns out.
sure beats pulling those carbs

 

Geez, Polock you're an optimist. But you're right.

While that should work running at 1600 or 1800 is no longer "idle" so if you do get it reasonably sync'ed using this trick, be sure to re-check it once you get the idle back down.

So have you checked the float levels or did that get skipped too?

 

BigFitz, Be patient as all this tuning stuff is new to me. Gotta start somewhere. One thing I am quickly learning is not to take any "shortcuts".
Armed with the invaluable how to write ups on this forum I am quickly losing my fear of messing with carbs too.
I pulled the rack at 4:30 am, Had the bench sync done an hour later.
Checked the float levels per the forum instructions with a level, fuel, and clear tubes and they are right on the money.
The rack was back in by 8:00. Those old rubber boots sure gave me a hard time-even with a hair dryer. I wiped the boots down with WD40.
The bike now purrs like a kitten even down to under 800 rpm.
Will do a vacuum sync this afternoon.

Thanks for the help!

Maz

 

TA-DAA!!!

Good job. Things really DO work when you go step by step and in order; I learned it the hard way myself. As you've found out, shortcuts generally lead right back where you started.

BTW, too low of an idle is hard on the motor, oil-pressure wise. Set it at 1050rpm when you're all done.

Wanna talk brakes now?

 

I set the idle to 1050 rpm. I just wanted to see how low it would idle.
Already did the rear and front brakes including replacing the ORIGINAL front brake lines. The rear brake shoes were toast and on the verge of delaminating. Did that before I started riding it.
My next project is replacing the clutch.
I'll be putting in wear and friction plates as well as springs.
Also a naw clutch cable while I'm at it.
The PO used Castrol GTX, but the car oil version.
That is about all the PM he really ever did to it.

Thanks again.

Maz

 

Good going. Clutch is a piece of cake, with immediate tangible results.

Ride safe--- Fitz

 

Here is me stealing in on this thread.
I have the same idle problem on my 1981 xj650 (non-yics, i think)

After the engine gets warmed up it revs high, around 5-6k and stays there of dwindles slowly to idle.

I just cleaned my carbs and replaced all seals, including the ever so important throttle shaft seals.

I am also certain that there are no airleaks between the head and the carb. The engine does not rev anything when I probe with propane gas.

The butterfly valves have all been synched and are se so that the idle hole and next hole after that shows, which is the most closed I could get them (I am referring to these holes http://xjbikes.com/Forums/viewtopic/t=1 ... heory.html )

The way I figure is that too much air and fuel is reaching the engine somehow.
If its not the throttle shaft seals, not the intake boots and not via the butterfly valves WHAT can it be?!

I still have not had time to look at the valve shims but the way I figure the problem is that air is slipping in somewhere.

I greatly appreciate your help and hope that none is offended because I used this thread instead of posting a new on the same subject.


/Ivar Nelson
Sweden

 

It sounds like you are still not in sync. You CANNOT DO a running vacuum sync unless your valves are in spec.

You also need to verify your float levels using fuel and clear tubing.

Gotta go back and get the steps you missed.

SO:

-Valves in spec. FIRST.
-Float levels verified and adjusted if necessary.
-Running vacuum sync.